Question

Design and analyse of a circuit which turns a DC motor at a speed which is proportional to how much a temperature is away from a set temperature, and turns:

Clockwise when temperature is greater than (say) 25 degrees C.

Anticlockwise when the temperature is less than (say) 20 degrees C.

Such a circuit might be used to regulate the temperature of a room by turning a ceiling fan to move warm air in/out of that room (using the roof cavity).

Report with following details

1. A full Block Diagram showing all from Input to Output.

2. Design calculation for each block

3.Full parts list

4. Circuit diagram

Answer 1

2.calculation for each block:

A) Thermistor: A thermistor is an electronic component that exhibits a large change in resistance with a change in its body temperature. The word “Thermistor” is actually a contraction of the words “Thermal Resistor”. The thermistors, which are to be described herein are ceramic semiconductors and have either large positive temperature coefficient of resistance (PTC) devices or large negative temperature coefficients of resistance (NTC). Both types of thermistors (PTC and NTC) have definite features and advantages which make them ideal for certain sensor applications. In this circuit, NTC type Thermistor of 1K at 25°C is used.

1) NTC Thermistor:The NTC thermistors are composed of metal oxides. The most commonly used oxides are those of manganese, nickel, cobalt, iron, copper and titanium. The fabrication of commercial NTC thermistors uses basic ceramics technology and continues today much as it has for decades. In the basic process, a mixture of two or more metal oxide powders are combined with suitable binders, are formed to a desired geometry, dried and sintered at an elevated temperature. By varying the types of oxides used, their relative proportions, the sintering atmosphere and the sintering temperature, a wide range of resistivity and temperature coefficient characteristics can be obtained.

2) Thermistor Basic Operation Assuming, as a first-order approximation, that the relationship between resistance and temperature is linear, then:

Thermistors can be classified into two types, depending on the classification of . If is positive, the resistance increases with increasing temperature, and the device is called apositive temperature coefficient (PTC) thermistor, or posistor. If is negative, the resistance decreases with increasing temperature, and the device is called a negative temperature coefficient (NTC) thermistor. Resistors that are not thermistors are designed to have a as close to 0 as possible, so that their resistance remains nearly constant over a wide temperature range.

3. componets:

You can use the components specification as per your need.

circuit diagram: